The present invention relates to x-ray sources, particularly to compact x-ray sources, and more particularly to a miniature x-ray source having millimeter scale size and capable of producing broad spectrum x-ray emission over a wide range of x-ray energies.
X-rays are typically produced in an assembly consisting of a vacuum housing, a high voltage feedthru, a high voltage connection to the feedthru, an anode, and a cathode. The assembly operates by applying a high voltage across a gap between the anode and the cathode. Electrons are emitted by the cathode and accelerated by the high voltage to the anode. The electrons impact on the anode and create both broadband and line radiation through collisional excitation of the atoms within the anode. The x-rays are emitted from the anode and propagate through the vacuum housing to be used for any given application. The vacuum housing must be highly transparent to the x-rays or have a high transparent window mounted in it to allow the x-rays to escape for use. The entire assembly is under vacuum to allow for efficient transport of the electrons from the cathode to the anode and to prevent a gas discharge or an electrical arc from forming, which would significantly reduce the voltage across the gap (reducing the x-ray energy) or destroying the assembly. Efficient production of x-rays and the production of x-rays with sufficient energy (5-40 keV or higher) for a wide range of applications requires the use of high voltages (5-40 kV or higher). The fabrication of compact x-ray sources has not been readily attainable due to the need to have high voltage over extremely small dimensions (xcx9c1 mm), high vacuum in extremely small volumes (cubic mms), and a high voltage connection of extremely small size (xcx9c1 mm).
Recently, an x-ray xe2x80x9ccatheterxe2x80x9d was designed which comprises a flexible catheter shaft having an x-ray unit coupled to the distal end thereof. Such an approach is described in Application PCT/US96/3629 filed Aug. 22, 1996 (International Publication No. WO 97/07740 dated Mar. 6, 1997).
The present invention provides a solution to this need by the use of a miniature x-ray source having high voltage over small dimensions, high vacuum in small volumes, and a high voltage connection of small size. The miniature x-ray source of this invention comprises an anode having a curved end, a cathode, a high voltage feedthru, a highly x-ray transparent vacuum housing, a high voltage connection to a high voltage cable, a pump-through member with vacuum pump-out channels that holds the cathode, and a crimp-off or vacuum tube containing a getter. The various components are interconnected by brazing or welding techniques.
It is an object of the present invention to provide a miniature x-ray source.
A further object of the invention is to provide an x-ray source of millimeter scale size.
A further object of the invention is to provide a miniature x-ray source capable of producing broad spectrum x-ray emission over a wide range of x-ray energies.
Another object of the invention is to provide a miniature x-ray source for remote operations wherein the source can be placed adjacent to a point of use, which improves the signal level and allows for local measurements in confined or remote locations. In addition, the x-ray source is capable of using high voltages without causing adverse effects at the point of use.
Another object of the invention is to provide a miniature x-ray source which includes a transparent vacuum tube containing a cathode, an anode, a high voltage feedthru, a getter, a pump-through member for initial vacuum pump down and crimp-off, and a high voltage connection for attaching a cable to the feedthru.
Another object of the invention is to provide a miniature x-ray source, including a highly x-ray transparent vacuum tube assembly constructed, for example, from boron nitride.
Another object of the invention is to provide a miniature x-ray source using either a cold (field emission) or a hot filament cathode.
Other objects and advantages of the present invention will become apparent from the following description and accompanying drawings. The present invention is an x-ray source capable of producing broad spectrum x-ray emission over a wide range of x-ray energies. The miniature x-ray source has a wide range of applications, such as the treatment of arterial restenosis, cancer tumors, and for material analysis, since the source can be inserted into extremely confined spaces, such as inside the human body, inside an artery, or in close proximity to material to be x-ray analyzed. The x-ray source consists of an anode having a curved configuration, such as a tungsten ball on the end of a tungsten shaft; a cathode, such as a diamond-coated tungsten substrate or graphite; a high voltage feedthru made of material such as ceramic or Maycor; a highly x-ray transparent vacuum housing made from material, such as pyrolytic boron nitride (PBN); a high voltage connection to a high voltage cable, such as a coaxial cable, a pump-through member or cathode mount with vacuum pump-out channels, and a vacuum tube for crimp-off containing a getter.